Minimum/Optimal Rudder sizing

[cyberbadger]

Hi,

Nyitra's launch is coming soon, and I am looking at a tiller probably first, and then over the winter I could upgrade it to steer by wheel.

A friend gave me an idea, which I like, but I don't know if the scale is correct to be efficacious.

Could you use two nice wooden paddles in front of the propellor connected by linkages as steering? Or is the area/cross sectional area on a paddle too small for a 24 ft launch?

As you can see these are roughly 20 inches x 6 inches:



-CB

[fredrosse]

Twin paddle rudders should not be placed forward of the propeller, if used they definitely should be aft of the prop.

A fairly simple, and effective rudder can be made from a 18 x 24 inch piece of sheet metal. Make a 170 degree bend with generous radius on the upstream end of the rudder (18 inch direction, giving two sides, each 12 inches x 18 inches) pop rivet the trailing edge of the rudder with a sharp exit, like typical fish fin shape.

The rudder shaft is made from a piece of 1 inch pipe, as shown in the attached picture. Four long bolts, (6 inches long, spaced at 4 inch center to center) running fore and aft, extending a few inches forward and a few inches aft of the pipe, with nuts tightened onto the pipe, plus nuts tightened together at the ends of each bolt. These bolts transfer the torque of the rudder to the rudder shaft.

Slide the sheet metal rudder over the shaft, and Pop rivet the rudder to the pipe shaft. Then fill the voids with automotive body putty, (Bondo in the USA), or better yet, Bondo Hair (very strong). 30% of the rudder area forward of the shaft, 70% aft. Dress the Bondo edges, make it pretty, and paint the assembly.

I built a rudder like this, using some scrap 18 gauge sheet metal, and it is 12 years now, still holds up very well. The bearings for the shaft support can be wood, the 1 inch pipe will turn nicely in a wet wood bearing.

[fredrosse]

A better profile, still easy to make.

[cyberbadger]

I like your design and am thinking of going with that general plan.

A couple questions:

Twin paddle rudders should not be placed forward of the propeller, if used they definitely should be aft of the prop.

Is it because Nyitra is a 3 hull pontoon and not a displacement hull? I was thinking about the Chautauqua Belle. It has 2 rudder in front of it's paddlewheel...

30% of the rudder area forward of the shaft, 70% aft.

I read this several times and am looking at your drawings and am not understanding what these percentages are referring to....

-CB

[fredrosse]

Chautauqua Belle is a sternwheel propulsion boat. Rudders were placed there because that was the convenient spot, but those rudders are not very effective, sternwheelers with this arrangement are notoriously difficult to maneuver. Many actually added extra rudders behind the paddlewheel.

For a propeller driven boat, the issue becomes much worse, if the rudder deflects flow from the propeller, it would often foul up the propeller efficiency, while it could steer, it would be a generally inefficient setup. Although I suspect it would be convenient for your boat.

All of that information is regardless of whether you have a displacement hull or not, perhaps 9,999 in 10,000 steamboats are displacement type.

The 30% of rudder forward of the shaft is shown with the following drawing, hope you can understand this crude sketch.

[cyberbadger]

Fred,

Thanks for the info and the drawing. It's not a crude sketch, It just didn't click. Thanks!

-CB

[cyberbadger]

Fred,

Like This:

Rosse Insta-Rudder


It is a bit taller, but I thought it wouldn't hurt anything and this was the size available 24"x24" 0.025" Aluminum sheet.
1" pipe like you said, 6" long 3/8" bolts. That was about maybe 2-3hrs to make. And a real time saver for my very aggressive launch schedule. Thank you Fred!

Don't know how to use this stuff yet. Tips would be appreciated, I never used bondo before. I'll find some youtube videos...


-CB

[fredrosse]

Bondo Instructions:

Rubber Gloves.

Mix about a teaspoon of the stuff with a couple of drops of hardener, just to get the feel of things, how much working time you have, etc.

to get the stuff in the right places, use a cake icing rig, made from waxed paper with about 1/2 inch diameter orifice. That can get down into the bolt areas with the bondo.

If you go light on the hardener you can get 10 minute working time, and it will eventually fully harden, but perhaps a couple of hours to fully harden.

Unlike epoxy, the proportions of hardener and Bondo can be varied to extend or shorten the working time. Getting it down into the voids of this assembly is the difficult part, so get a feel for its work-ability before you start the rudder filling.

[cyberbadger]

1) I rivetted the sheetmetal skin onto the pipe. I ended up with a decent profile but a little bit of warp. Shoudn't be that noticable and i doubt it will really matter as far functioning as a rudder.

2) I taped the bottom shut and cracks with a mix of aluminum tape and kapton tape.

2) I am a big fan of great stuff, and I decided to product test a new product that claims to be the "Next Generation of Insulating Foam to Fill Gaps & Cracks": Loctite Tite Foam.

It claims 4X more density with more uniform structure. It "Seals out Water, Moisture & Pests". "More resistance to the elements without becoming brittle.", "Withstands Build&Material movement", "bonds to wood, metal, stone, brick, pvc"

Listen to Rosses first bondo instruction, wear gloves! I didn't. I've tried a bunch of thinners - the recommended one for Loctite Tite Foam is Acetone - which I found too late. It's sticking like an extra layer of skin sort of like superglue does.

You can lead a horse to water, but you can't make it drink I guess.

-CB/AKJ

[fredrosse]

The Great Stuff, expanding foam should work OK, especially the structural stuff, much stronger than the insulating foam. It will not be as strong as the Bondo,but unless the rudder strikes something hard it is probably OK.

See you learned about great stuff sticking irreversibly to skin. You are not the only one to have learned this the hard way!